Glossy reflections and smooth shading
There are two common ways for modeling rounded corners. One, using a bevel modifier. Two, using a subdivision surface modifier. Both have advantages.

Bevel Modifier:

The bevel modifier's main problem is the sharp edge it gives on each side of the bevel as seen in the image below. It can look very 3Dish when using highly reflective shaders. But the advantage is that it keeps a relatively low polygon count in comparison to subdivision surfaces and keeps a better curvature by maintaining a perfectly circular curve.

To reduce distortion in the reflections, one can add edge loops to correct the normals so that they face directly outwards. See image below.

Subdivision Surface Modifier:

The advantage to the Subdivision Surface (sub-surf) modifier is the smooth transition of faces that the catmull-clark algorithm creates. But, to get noon-distorted results, you must have a high subdivision level, Causing polygon counts to double or quadruple.

In the end, neither are perfect. But the sub-surf modifier will give better results. At the cost of your render speed.

An example of the subdivision method:


An example of the bevel method with added edge loops to improve normals: